[cryptonector]

Mainly because using monadic I/O trivially encourages you to write pure (deterministic) code for most of your programs, which makes it easy to write tests for them. Besides that, it's easy to write great libraries, which then makes the language very expressive. The downside is that the cognitive load for using it can be very high, but looking at C++ it seems clear that high cognitive loads are a feature across the industry, and here to stay.